Project Summary Three decades into the HIV epidemic, high HIV/STI rates persist among FSWs throughout the world, and research on this population in the U.S. is scarce. FSWs experience a unique set of vulnerabilities associated with structural factors such stigma, and unsafe work environments. These factors inhibit protective sexual behaviors and seeking of HIV testing, care, and treatment. HIV prevention approaches that address social and structural vulnerabilities to HIV infection among FSWs have demonstrated effectiveness worldwide. Yet in the U.S., structural HIV prevention interventions are scarce. Our research has found extensive structural vulnerability such as high rates of homelessness, hunger, and violence, as well as high rates of injection and noninjection drug use among street-based FSWs. We are currently in the 4th year of ?A structural HIV prevention intervention targeting high-risk women? (R01DA041243) ? the ?EMERALD? study - that focuses on developing and evaluating a unique and innovative structural intervention aimed to reduce the burden of HIV, STIs, and problematic drug use among FSW. We are requesting a supplement to support the actual and projected cost of the EMERALD cohort recruitment and follow-up. Briefly, recruitment and retention expenses are significantly higher than anticipated compared to our prior studies among FSW in Baltimore. At the current, time, the study population have proved to be less accessible to reach and to follow- up, which requires more time and effort from our field staff. Further, increasing rates of fatal overdose in Baltimore, consistent with the local and national opioid epidemic, are impacting our study population and sample. The supplement?s aims are the following. First, to enable continued expansion (350 to 385 women) and follow-up the EMERALD cohort to sufficiently examine the effect of exposure to intervention (SPARC Center) components on HIV/STI risk behaviors (e.g., drug use/unprotected sex), and HIV/STI cumulative incidence over time in FSWs in the intervention group (n=225) compared to those in the comparison group (n=160). Secondly, to examine correlates of nonfatal and fatal overdose in the EMERALD cohort (N=385) given higher than anticipated fatal and nonfatal overdose rates owing to the opioid epidemic. Through Aim 1, the requested supplement will allow us to both expand our sample as well as intensify follow-up efforts for the total study sample given the need for more staff intensive up efforts. Aim 2 will allow for a robust understanding of both nonfatal and fatal overdose deaths, examining the prevalence, incidence, correlates, and predictors of both self-reported nonfatal and confirmed fatal overdoses, the latter of which through the National Death Index from the National Center of Health Statistics.